Ultrasimple Multicolor Flashing LED

Nowadays, single-color and multi-color flashing LEDs are easily available, which obviates the requirement of external chips to produce fascinating lighting effects. What can we do with one piece of such a single color flashing LED, and two pieces of multicolor flashing LEDs?

Here is an ultrasimple circuit of an LED Globe wired around the evergreen timer chip IC 555. One advantage of this LED Globe is that it is a voltage-controllable flashing device, ready to work together with any microcontroller chip. This allows you to control the light pattern to a certain extent in tune with the output signal from an external microcontroller, too!

Multicolor Flashing LED Circuit Diagram:

LED Circuit Diagram

LM555 Datasheet:
Nothing new, here the 555IC (IC1-LM555) is wired as a monostable multivibrator (MMV) working on regulated DC5V supply. RC components R2(1K) and C2 (100uF) sets the monotime period. At the front end of the circuit, one single-color flashing LED (LED1-5mm Red) is connected across the power rail through a current limiting resistor (R1-1K). The pulse output available from this LED is directly fed to the trigger input (pin 2) of the 555 IC.

Flashing LED Circuit Diagram

The control voltage is driven to the control voltage terminal (pin 5) of IC1 through a resistor (R4-1K). For normal use, the control voltage can be generated from a 10K multi-turn potentiometer (P1-10K) as shown in the circuit diagram. Actually, any kind of DC voltage level generator can be used to control this circuit. It could come from a photoresistor voltage divider, sound to voltage converter,from a microcontroller,etc etc. The IC1 output (from pin 3) is then extended to two 5mm multi-color flashing LEDs (LED2&LED3) through a single current limiting resistor (R3-47R).

Multicolor Flashing LED Circuit Diagram
Multicolor LED Circuit Diagram

As you may well know, 555 IC turns on when its pin 2 is below 1/3VCC, and turns off when its pin 6 goes above 2/3VCC. These levels can be shifted either higher or lower than the nominal levels by applying a voltage at its pin 5. For example if we apply a higher +ve voltage, the turn off threshold is higher than the normal 2/3VCC. This trick is used in this circuit to produce pleasing (and fairly unpredictable) light patterns from the three LEDs. Try to enclose the finished circuit in a translucent globe for better attraction. Or try an artistic arrangement with the help of suitable light diffusers!

Test Report:
  • During testing, pulse reached at pin 2 of IC1 is of 1.2Hz frequency with near 47% dutycycle. The voltage swinging is in 1.4V to 2.1 V range (not very accurate measurement)
  • Voltage available at pin 5 of IC1 is from 0.8V (P1 fully counter clockwise) to 4.5V (P1 fully clockwise)
  • When P1 is in fully counterclokwise , LED2 is ON and LED3 is OFF. When P1 travels beyond its mechanical centre position LED3 also turned to ON state. When P1 is in fully clockwise, both LEDs are in ON state but now with a different pattern. Amazing visual effects created by the three LED combination is very difficult to describe in detail. Get ready to watch it yourself !.

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